1. Field of Invention
The present invention relates to rotors for dynamoelectric machines and particularly to methodology for building and then magnetizing a permanent magnet rotor assembly, wherein a magnet or magnet rotor body is mounted to a rotor shaft that contains an angular position reference feature, or “mechanical key,” and magnetization of the resulting rotor assembly, without regard to any complementary mechanical key on the magnetization fixture, nevertheless keys the resultant magnetic field to the rotor.
2. Prior Art
The manufacture of dynamoelectric machines entails some of the same basic challenges—and more—inherent in any typical machine manufacturing and/or assembly process. Of special consideration are factors relating to the use of permanent magnets, given the structural and magnetic properties of these, often fragile, materials. For example, when, and how, in the build process, are magnets magnetized? There would be great benefit if a rotor could be random-angle magnetized after assembly and the angular position of the resulting permanent magnetic field synchronized with a mechanical key in a shaft.
Permanent magnet magnetization strategy depends on a number of factors, including, but not limited to, energy product, desired number and orientation of magnetic pole pairs, mechanical complexity of the magnet and/or magnet rotor body, magnet composition, and size. In the process of manufacturing a dynamoelectric machine, there exist significant advantages in magnetizing the rotor assembly after magnets have been mounted and the assembly completed. Magnetization in this order can immensely simplify the assembly process. There is no comparison between handling magnetized magnets—especially those with high energy products—and handling un-magnetized, i.e., benign, magnets. Un-magnetized magnets do not have a propensity to slam against magnetic metal, against other magnets, or against operators who have any magnetic material(s) on their person—or who happen to let a finger wander between two unsecured magnets. Un-magnetized magnets also do not affect nearby electronic equipment such as computers or operator terminals used during the assembly process. Anyone who has been around magnets knows that the handling of magnetized magnets involves inordinate care and process safeguards. Otherwise, consequences can be severe or catastrophic.
Magnetization of assembled permanent magnet rotors can be quite challenging, especially when the assembly comprises high energy product magnets and a keyed shaft. Prior art is replete with examples of permanent magnets or magnet rotor bodies keyed to a shaft; however, the inventions described therein are methods for safely arresting relative axial and/or rotational movement between the permanent magnet(s) or rotor body and the rotor shaft. For example, U.S. Pat. No. 4,060,745 (1977) to Linscott discloses a method for securing an annular permanent magnet against axial and rotational movement, relative to a shaft, while minimizing stress on the rotatable permanent magnet. The primary structural elements used to accomplish this task are depicted in FIGS. 1A and 1B, wherein “magnet 12 is prevented from rotating with respect to the shaft 10 by means of a pin 28 . . . or a key 34 . . . and shoulders 18 and 22 cooperate to axially retain the magnet 12 on the support surface 16,” and “a flexible material 32 is interposed between” contiguous components to protect the magnet 12 from the effects of compressive stresses.
In fact, inventors have taken elaborate measures to arrest relative rotational and axial motion between rotor bodies and shafts, while safeguarding the permanent magnets. FIG. 2 relates to U.S. Pat. No. 7,737,592 to Makino, et al., (2010), and depicts a cross-sectional view of a cylindrical rotor assembly. Said patent discloses a complex assembly in which relative rotational motion between a keyed rotor shaft 21 and a rotor core 22 is restricted when said shaft 21, with shaft side axial groove 214 is arranged concentrically with an axis J1 of said core 22, with core side axial groove 223, such that the axial grooves line up to form an axial hole and a movement restriction member 28 is inserted into said hole. Additionally, relative rotational movement between a plurality of magnets 23 and the shaft 21 is restricted via the insertion of said magnets 23 into a corresponding plurality of axial holes 221 in the core 22. Axial motion is restricted equally rigorously.
Even inventions with methods that comprise steps of providing structural elements other than keyed shafts have been used to securely mount a rotor body to a rotor shaft. For example, U.S. Pat. No. 3,246,187 to Iemura (1966) discloses a structure that entails use of adhesive and axial ridges, or knurl, placed circumferentially on a non-keyed shaft. FIG. 3 is a cross-sectional view of the cylindrical rotor and a front view of the cylindrical shaft. It includes one adhesive layer 9, retainer disks 6, a magnet core 1, an axial bore 3, and a rotor shaft 4, with knurl 5. Iemura claims that his invention offers a much higher binding strength “than that of conventional rotors in which the retainers and the rotor body are joined to each other and to the rotor shaft with separate adhesive layers, and is enough to prevent the rotor from being damaged by any mechanical shock.”
As noted, the patents cited above—and countless other patents—deal with the object of attaching a permanent magnet or magnet rotor body to a keyed or non-keyed shaft to prevent relative motion of components. Another object not obvious or implied in any of these patents, but, in some cases, of equal or greater relevance, relates generally to magnetic—not mechanical—considerations, and specifically to a method for effecting on an already assembled rotor a permanent magnetic field keyed to a keyed shaft. The major disadvantage of the inventions described therein is that they lack this feature.